DOORS , WINDOWS & FITTINGS
WINDOW ENERGY RATINGS OR U-VALUES ?
BY WOJCIECH BROŻYNA - MD OF ALUPROF UK
Back in 2005 , the Glass & Glazing Federation ( GGF ) took over the British Fenestration Rating Council ( BFRC ) and then gained Government acceptance of the then new , Window Energy Rating scheme ( WER ’ s ). At the time these ratings became a means of compliance with Building Regulations . As all WERs are based on the same standard sized window , and enable direct comparisons across various manufacturers ’ products , this helps customers in product selection . By combining a window ’ s solar gain benefits , its air permeability and thermal efficiency in a simple calculation offers an easily understood ‘ banding ’ of performance , the result of which is something that the wider public already understands from the sale of domestic electrical goods . As we now move to higher performance windows and the need to thermally enhance our complete building fabric , are WER ’ s still the best measure ?
With the next announced change in Building Regulations just two years away , when the Industry will be expected to offer window U-values of below 1.0 will this mean that the current WER banding becomes mostly obsolete ? When first launched , the WER scheme offered ratings across a band of A to E , more recently the band is running with two further ‘ A ’ bands of ‘ A +’ and ‘ A ++” which recognise higher performance windows . Will bandings need to be realigned if we decide to continue to use them in the future ?
generate more energy than they need , producing excess ‘ green energy ’ which can then be used elsewhere .
There are various schemes and specifications that enable architects to construct or renovate buildings to meet very high thermal standards whilst maintaining a healthy internal environment . Passivhaus is a well known specification which is rapidly becoming the specification of choice for architects . Based on a ‘ fabric first ’ approach , the complete building fabric must be carefully designed with high insulation materials taking great care to eliminate cold bridging either inside a building element or where various building elements interface . One of the challenges of good fabric design within Passivhaus , is the window frame interface to the structural reveal of a building , particularly in an existing building .
Whilst not all our future buildings will be built to the Passivhaus specification , the basis of this specification is logical and there will be alternate specifications agreed upon . Scotland has already agreed that in a couple of years all new homes will be built to their version of a Passivhaus standard .
So , whilst there has been a swing in the past to use WERs as a simple tool of energy performance , the industry will swing back to using the U-value as this measure will be needed to design good thermally efficient spaces within buildings . In future , it is not going
In reality , the choice of window performance on WER ’ s alone is flawed . When the energy performance label was introduced for electrical goods back in 1995 products bought and used across the UK would perform very much the same in any home , the same cannot be said for WER ’ s . Windows chosen on a WER will be made to measure , in various configurations , installed in various constructions , located in different geographic locations and in various orientations . Windows facing South will realise a high solar gain , whilst those facing North will experience very little so , the ‘ best ’ WER performance window chosen may not be the best performing in use and therefore not the most cost effective choice .
It is well understood today that a holistic optimisation of the complete building fabric is more beneficial in terms of energy and environmental savings than a component-by-component approach . The provision of a calculated window U-value for a given configuration can then be used in the formulation of a building ’ s thermal performance , a WER cannot .
Homes in the future will have to be built to and refurbished to a very high thermal standard which then require very little energy to heat , indeed , some high performance buildings could actually
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